1. Field of the Invention
The present invention relates to a sheet processing apparatus for performing sheet processes such as a punching process to a sheet, a control method for the sheet processing apparatus, a sheet processing method, and storage media storing programs for executing the methods.
2. Description of the Related Art
Sheet processing apparatuses are known, which perform sheet processes such as sorting, binding, loading, and punching on sheets discharged from an image forming apparatus and each having an image formed thereon.
An example of a sheet process using a sheet processing apparatus such as one described above is a punching process for punching to sheets. For example, a punching method has been proposed, which stacks sheets on a processing tray and punches a bundle of stacked sheets. This method, however, has disadvantages: For example, the bundle of sheets may be too thick to be punched depending on the number of sheets in the bundle to be processed, and taking such a problem into consideration, a large-scale punching unit must be provided. Further, during the punching process, it is impossible to convey a new sheet, or depending on the capacity of the punching unit, the punching process has to be carried out in a plurality of steps, which necessitates suspension of conveyance of sheets from the image forming apparatus. Consequently, the processing speed cannot be increased easily.
To solve the above described problems, a method has been proposed, which provides a punching unit on a sheet conveyance path and conveys a sheet therealong while sequentially punching to the sheet.
This method, for example, provides on a sheet conveyance path a punching unit comprised of punches and dies, and synchronizes the sheet conveyance speed with the punch speed to execute the punching process without stopping the sheets from being conveyed. This method has the advantage that the sheet processing time does not increase even when the punching process is executed.
When sheets are punched while being conveyed as described above, the punching position should desirably be adjusted before actually punching the sheet, so as to punch the sheet being conveyed at an appropriate position thereof. More specifically, it is desirable to carry out both adjustment of the punching position in the sheet conveying direction and adjustment of the punching position in a sheet width direction at a right angle to the sheet conveying direction, followed by carrying out punching of the sheet. The adjustment of the punching position in the sheet conveying direction is carried out by, for example, detecting appearance of a leading end (in the sheet conveying direction) of the sheet being conveyed and controlling timing for execution of the punching process based on a result of the detection to thereby adjust the punching position in the sheet conveying direction. On the other hand, the punching position in the sheet width direction at a right angle to the sheet conveying direction is adjusted by, for example, detecting an end position of the sheet being conveyed in the sheet width direction and moving and adjusting the punching unit in the sheet width direction based on a result of the detection to thereby adjust the punching position in the sheet width direction. Both adjustments are carried out based on the sheet to be punched while the sheet is being conveyed, as in an actual punching process.
The apparatus of this type can convey different types (for example, different sizes) of sheets and can execute the above described punching process on various sheets. However, the same manner of adjustment of the punching position in the sheet width direction at a right angle to the sheet conveying direction is applied whatever types of sheets are to be punched.
According to the above described method, however, both the adjustments of the punching position and the punching process depending on these adjustments are carried out while sheets are conveyed. Consequently, if, for example, a sheet to be punched skews while being conveyed, the amount of skewing of the sheet at the time of actual punching is larger than that at the time of execution of the adjustment of the punching position in the sheet width direction. That is, an appropriate position to be punched may change gradually during the sheet conveyance, whereby the punching position in the sheet width direction at a right angle to the sheet conveying direction is shifted. In spite of the possibility of such a phenomenon, the same manner of adjustment of the punching position in the sheet width direction is applied for any types of sheets. This leads to, for example, while a disadvantage that sheets of a certain size do not substantially deviate in punching position, sheets of another size significantly deviate in punching position so that the punched sheets are useless, resulting in a waste of resources.